ABSTRACT A novel phosphatidylinositol-3 kinase (PI3K) that appears to play a key role in cell transformation and growth has recently been described by Cantley and co-workers. Over the past 6 months, the principal investigator, while on sabbatical in Cantley's laboratory, has demonstrated that insulin dramatically increases the activity of this enzyme in CHO cells transfected with human insulin receptors (CHO-HIR). The proposed studies will examine the basis for this effect, the physiological relevance of PI3K will be explored. The specific aims are (1) To complete the characterization of the time-course and dose response to insulin of PI3K in CHO-HIR, both in vitro (anti-P-tyr and anti-insulin receptor antibody immunoprecipitates) and in intact cells. (2) To compare the response of CHO-HIR to those of CHO cells that are deficient in insulin receptors or have been transfected with mutant receptors that do not express tyrosine kinase. (3) To evaluate the relation of PI3K activation to acute and long- term metabolic effects of insulin. (4) To test the hypothesis that activation of its intrinsic tyrosine kinase causes the insulin receptor to tissues and determine whether it is altered by ageing or nutritional and hormonal perturbations. These studies should provide important information about the physiological relevance of PI3K and its regulation by insulin. Based on our preliminary data, we also anticipate they will provide new insights into the mechanism of signal transduction by insulin receptor kinase.